1. Field of the Invention
The present invention relates to a gas discharge panel display apparatus and a method for driving a gas discharge panel used for image display for computers, televisions, and the like. The invention particularly relates to an AC plasma display panel which writes an image by accumulating a charge in a dielectric layer and illuminates discharge cells by performing a sustain discharge.
2. Related Art
In recent years, gas discharge panels including plasma display panels (hereafter referred to as PDPs) have become the focus of attention for their ability to realize a large, slim and lightweight display apparatus for use in computers, televisions, and similar. In these gas discharge panels, a PDP produces an image display by selectively illuminating discharge cells arranged in the form of matrix.
PDPs can be broadly divided into two types: direct current (DC) and alternating current (AC). AC PDPs are suitable for large-screen use and so are at present the dominant type.
Discharge cells in an AC PDP are fundamentally only capable of two display states, ON and OFF. Here, a field timesharing gradation display method in which one frame (one field) is divided into a plurality of sub-frames (sub-fields) and the ON and OFF states in each sub-frame are combined to express a gray scale is used.
For image display in each sub-frame, an ADS (Address Display-period Separation) method is employed. In this method, each sub-frame is composed of the following sequence: a set-up period, a write period, a discharge sustain period, and an erase period, as shown in FIG. 25. In the write period, a wall charge is accumulated in the discharge cells which should be illuminated, to write an image. In the discharge sustain period, AC sustain pulses are applied to all discharge cells. The voltage of the sustain pulses applied here is set within such a range that causes a discharge to occur only in the discharge cells where the wall charge has accumulated (usually in a range of 150V to 200V).
This illumination principle is basically the same as that of a fluorescent lamp. When a sustain pulse is applied to cause a normal glow discharge, ultraviolet light (Xe resonance lines with a wavelength of 147 nm) is generated from Xe and excites a phosphor to emit light. However, since the efficiency of the conversion from discharge energy to ultraviolet light and the efficiency of the conversion from ultraviolet to visible light in a phosphor are not high, a PDP cannot produce as high brightness as a fluorescent lamp.
Also, there is the demand for high-definition PDPs, just as other types of display (high-definition television with high resolutions of up to 1920×1080 pixels at full specification is currently being introduced). However, such a high-definition PDP is likely to suffer further decreases in luminous efficiency. In view of these points, an important issue in the PDP technology is to increase luminous efficiency (i.e. the amount of brightness with respect to the amount of power). To achieve this, techniques of improving structures of PDPs and techniques of recovering currents (reactive currents) which do not contribute to ultraviolet light emission are being developed. Also, techniques for suppressing the occurrence of reactive currents are being sought.
Furthermore, a rectangular wave is generally used for sustain pulses, as shown in FIG. 25. The leading edge of the rectangular wave is sharper than the leading edge of a wave such as a trigonometrical function wave. Accordingly, using a rectangular wave for a sustain pulse enables a discharge to start comparatively soon after the leading edge of the sustain pulse, with it being possible to display an image with relative stability.
However, when applying a sustain pulse, there is a certain probability that so-called “discharge delay” occurs. The discharge delay refers to a substantial time delay from the leading edge of the pulse to the start of the discharge. In particular, the discharge delay tends to occur for a sustain pulse which is first applied in a discharge sustain period.
This discharge delay causes a drop in image quality. Which is to may, if there is a certain probability of occurrence of discharge delay in a PDP in which a large number of discharge cells are aligned, discharge delays may occur in part of the discharge cells which are to be illuminated. When this happens, illumination failures will result, and the quality of the displayed image will decrease. Therefore, techniques for preventing discharge delays are desired, too.